1. Field of the Invention
The present invention relates to a signal reproducing apparatus which can reduce the rotational speed of the heads compared with the past when playing back and recording a magnetic tape.
2. Description of the Related Art
For example, in a video tape recorder (VTR), when playing back and recording a VTR tape, sometimes variable speed playback and variable speed recording are performed at speeds different from the normal playback speed and recording speed.
A VTR tape, as shown in FIG. 1A, is provided with tracks of a pitch Mt at a track angle of .theta.3 with respect to the longitudinal direction of the tape. These tracks include plus azimuth tracks A and minus azimuth tracks B alternately positioned with each other. The tracks A are read by the head A provided at the position of the upper drum section shown in FIG. 1A and the tracks B by the head B.
In such a VTR tape, when the upper drum section is rotated in the still state where the tape is not being transported, the lead angle of the heads A and B is .theta.1, but if the tape is transported at 1.times. speed (normal speed) and the upper drum section of the VTR tape scanner is made to rotate at a rotational speed of 30 rps, the scanning angle of the heads A and B becomes .theta.3 and so the tracks A and B are accurately scanned.
The lead angle .theta.1 is for example 5.degree.56'7.4" in the case of the VHS format and 4.degree.53'6" in the case of an 8 mm format.
The track angle .theta.3 and pitch Mt in a VTR tape are defined as the format.
However, when playing back or recording the VTR tape shown in FIG. 1A at a 2.times. speed (double speed) by the lead angle .theta.1 of the heads A and B, if the rotational speed of the upper drum section is not changed and only the transport speed of the VTR tape is doubled, then, as shown in FIG. 1A, the scanning angle of the heads A and B becomes .theta.2 and, as shown by the horizontal lines in FIG. 1B, only half of the tracks can be scanned.
At this time, if the rotational speed of the drum is doubled, then all of the tracks of the VTR tape can be scanned, but the frequency handled doubles and a need is created for raising the frequency characteristics of the circuits. Further, it suffers from the disadvantage of the hitting to the tape by the head tips, that is, the vibration caused in the tape when the heads A and B move away from and toward the VTR tape.
In particular, during 4.times. speed (four times speed) playback and recording, the rotational speed of the upper drum section becomes 120 rps and the frequency handled becomes higher, so it suffers from the disadvantage that fabrication of the circuits becomes difficult.
To overcome the above-mentioned disadvantages, there is known the dynamic tracking head (DT) system, in which use is made of a drum with a normal lead angle and diameter, but the number of heads is doubled so that even when the transport speed of the tape is doubled, all tracks of a VTR tape can be suitably scanned while causing the upper drum section to rotate at a rotational speed of 30 rps (revolution per second).
By using the dynamic tracking head system, even for example when performing 4.times. speed playback and/or 4.times. speed recording, the rotational speed of the upper drum section may be made 60 rps and circuits of a frequency able to be handled can be fabricated.
If the dynamic tracking head system is used, however, a circuit for driving the dynamic tracking heads becomes necessary. Further, a position sensor becomes necessary for controlling the head height when recording. Therefore, it suffers from the disadvantage of the construction of the drum becoming complicated.
Further, in a VTR tape, as shown in FIG. 1A, pilot signals having a frequency characteristic of a frequency f0 are recorded on the even number tracks, while pilot signals having frequency characteristics of frequencies f1 and f2 are recorded alternately on the odd number tracks.
In a VTR, when a head scans an even number track, the ratio between the f1 pilot signals and f2 pilot signals recorded on the odd number tracks at the two sides is detected so as to perform tracking servo control, that is, ATF servo control. When scanning an odd number track, ATF tracking servo control is not performed.
Therefore, when scanning an odd number track, the track scanning precision depends on the precision of the relative mount height and distance between the head scanning the even number track and the head scanning the odd number track.
Accordingly, when the precision of the mount heights of the two heads is low or when the distance between the two heads is long, the tracks subjected to positional control by the AFT servo control can be suitably scanned, but the other tracks suffer from the effect of head height error due to vibration of the drum face and so the problem arises of tracking deviation.